Dose of anti D for antenatal prophylaxis in Rh- negative nonimmunized females:
**Core Concept**
The administration of anti-D immunoglobulin to Rh-negative nonimmunized females is a crucial measure to prevent the formation of anti-RhD antibodies during pregnancy, thereby minimizing the risk of hemolytic disease of the newborn (HDN) in subsequent pregnancies.
**Why the Correct Answer is Right**
The recommended dose of anti-D immunoglobulin for antenatal prophylaxis in Rh-negative nonimmunized females is 300 micrograms, administered between 28 and 32 weeks of gestation. This dose is sufficient to neutralize any potential fetal RhD-positive red blood cells that may enter the maternal circulation during pregnancy, thereby preventing the formation of anti-RhD antibodies. The administration of anti-D immunoglobulin at this gestational age is crucial, as it coincides with the period of maximal fetal-maternal hemorrhage.
**Why Each Wrong Option is Incorrect**
* **Option A:** 150 micrograms - This dose is insufficient to provide adequate prophylaxis against the formation of anti-RhD antibodies.
* **Option B:** 450 micrograms - This dose is excessive and may increase the risk of adverse reactions without providing additional benefit.
* **Option C:** 1,000 micrograms - This dose is far in excess of the recommended amount and would likely cause significant adverse effects.
**Clinical Pearl / High-Yield Fact**
RhD-negative nonimmunized females should receive a single dose of 300 micrograms of anti-D immunoglobulin between 28 and 32 weeks of gestation to prevent the formation of anti-RhD antibodies during pregnancy.
**Correct Answer:** D. 300 micrograms